John Marsden’s superlative “Tomorrow” series set the tone for young adult political/social thrillers. Now there are two new adventures: Emmy Laybourne’s “Monument 14,” set in a slightly futuristic Monument, Colorado; and “No Safety In Numbers” by Dayna Lorentz.

In “Monument 14,” Labourne’s debut novel, an apocalyptic event strands 14 school children in a Target-like megastore. The crisis reshapes the social dynamics of the older students, not quite reversing the pecking order but definitely setting the popular jock and the bully back on their heels.

With one foot in childhood — yay! Sundaes for breakfast — and the other in adulthood — upon realizing that the store’s air conditioning system is sucking in noxious bio-weapon chemicals, the kids figure out how to seal off the outside air intake — “Monument 14″ is unsettlingly plausible, or plausibly unsettling. (A couple of kids takes advantage of the store pharmacy and liquor departments, but other kids prove to be surprisingly mature and pragmatic.) It’s a fast, taut thriller for readers aged 13 and up.

“No Safety In Numbers” also traps a lot of people, of all ages, in a suburban mall. The premise: Terrorists have parked a bomb somewhere in the mall’s air ducts. It’s up to a member of Congress (God help us) and mall cops and some haz-mat feds to solve the problem of finding the bomb and keeping peace among the mall’s inadvertent inmates.

The story is told by several narrators, which clouds the tension as author Lorentz establishes the characters’ back stories. The bomb threat becomes almost an afterthought to subplots that involve football rivals, a Queen Bee/wanna be dynamic, and a complicated family relationship.

But it’s an interesting and possibly prescient premise. Could the next attack within US borders take place in a facility that has become so iconic of this country? Ages 12 and up.